Method for addressing the participants of a bus system

ABSTRACT

In the method for addressing the participants ( 1  to  4 ) of a bus system, the central control unit ( 12 ) connects the bus line ( 12 ) to one potential of the operating voltage, while each participant tries to pull the bus line ( 12 ) to a reference potential, normally the operating voltage, wherein, due to the current source behaviour of the switch ( 26 ) placing the bus to the operating voltage, a current is detectable by a detector ( 22 ) arranged in the bus line and associated with the participant ( 1  to  4 ). When the participant detects this decrease of current, said participant switches off its switch ( 26 ). Due to time-defined slow connection of the switched current sources, this process takes place sequentially within a group of participants until the last participant is reached. The detector associated with this participant does in no case detect a current, such that, after elapse of a predeterminable on-period, the switch ( 26 ) of this participant ( 1  to  4 ) is still open. Thus one of the participants from the group of all participants is specified such that an address can now be allocated to this participant. During further addressing cycles the remaining participants are subjected to the same process, wherein the switch of the participant already addressed remains open all the time.

The invention relates to the addressing of (any number of) participants of a bus system comprising a control unit, a bus starting from the control unit and a plurality of participants which are sequentially connected to the bus, the method being an advancement of the method proposed in DE 101 47 512 A1.

For minimizing the wiring complexities, for example in vehicles, it is more and more common practice to transmit the control signals for driving actuating elements via a bus to which, besides a control unit, the drive units for the actuator devices of the individual participants are connected. Combined to form a bus system are, for example, the actuator devices of a vehicle air conditioner, the window lift or the front seats of a vehicle. To enable the control unit to selectively drive one or a plurality of actuators, addresses are assigned to said actuators. So far, the addresses have been e. g. stored in the participants by programming or assigned to the participants via plug or PIN coding. While programming is relatively unproblematic during the manufacture of a vehicle, this is more complicated when the overall participant, i. e. the actuator device plus the drive unit, is, for example, replaced in a repair shop. Further, with regard to the logistics it is necessary that defined placement sequences are adhered to, which involves service inconvenience and the supply of pre-programmed (pre-addressed) components, which runs counter to the identical-part principle. Further, the plug coding may lead to malfunction. Finally, it is also possible to realize the self-addressing of the participants of a bus system via switches for serially separating the bus connections between the participants. The drawbacks encountered in this regard are in particular the electrical disconnection of the bus line via active components and the large space requirement for bus systems which comprise a lot of participants.

Automated address allocation methods for bus systems are known from EP 0 854 609 A1, DE 196 47 668 A1, DE 44 04 962 C2, DE 44 28 502 A1, WO 97/45983 A1 and DE 197 56 564 A1.

Finally, from DE 40 38 992 C2 a method is known where the addresses of the components of a danger-warning system are automatically assigned. Addressing is effected from the participant arranged closest to the central unit to the participant arranged farthest away from the central unit. Each participant comprises a resistor in each of the two wires of a warning-system primary line, and a plurality of electrical and electronic components between the two wires. Further, each participant is provided with a short-circuit switch for short-circuiting the two wires. When a switch is short-circuited, the voltage drop across the two aforementioned resistors (with a measuring current being impressed onto the warning-system primary line) can be measured. All participants are arranged in series in the warning-system primary line.

At the beginning of the addressing process a central control unit transmits a short-circuit signal for closing the short-circuit switches of all participants which have not been addressed so far. Then a measuring current is impressed which is designed to cause a voltage drop in the first participant, as seen from the central unit, (i. e. a participant arranged closest to the central unit) of the group of participants not addressed so far. Thereafter an address data signal is applied to the warning-system primary line. That participant, to which no address has been assigned so far and which previously detected a voltage drop, takes this address data signal into its address memory. Subsequently the short-circuit signal is allocated for the purpose of further addressing, wherein the short-circuit switch of the participant addressed before is not closed but rather the short-circuit switches of all participants not addressed so far are activated. When the measuring current is being impressed, it generates a voltage drop, which is to be detected, in that participant of the group of participants not addressed so far that is now arranged closest to the control unit, such that this participant, in the next phase in which an address data signal is applied to the warning-system primary line, stores this address in its address memory and is thus also addressed. This process is continued until the last participant is addressed.

This known method proceeds from the ideal assumption that due to short-circuiting of the two wires of the warning-system primary line the overall measuring current flows via the short-circuit switch of that participant of the group of participants not addressed so far that is arranged closest to the central control unit. In the practice, electronic switches, which are used as short-circuit switches in the known method, have an on-resistance which is not negligible. Therefore a portion of the measuring current flows through the short-circuit switch of the adjacent participant not addressed so far and generates a voltage drop across this participant's resistors. It is thus necessary not only to take into account the fact that a voltage drop has been detected but also to detect the magnitude of this voltage drop. Further, it must be taken into consideration that, the farther away a participant not addressed so far is arranged from the central control unit, the more the measuring current and thus the detectable voltage drop are reduced. The reason for this is the fact that the measuring current must flow via the closed short-circuit switch of a participant located relatively far away from the central control unit via the resistors arranged in the wires of the warning-system primary line of the participant already addressed and disposed before the former participant. Evaluation and reliable detection of the voltage drops according to the known method are thus not trivial and involve high circuit complexities and programming effort.

In the German Patent Application DE 101 47 512 A1 a method is proposed which eliminates the problems described with regard to DE 40 38 992 C2. However in a specific embodiment the problem of relatively high BUS flows is encountered. These flows occur when the resistance of the pull-up 30 or the pull-down 40 of the central control unit 14 is lower than the joint resistance of all switches 26 of all participants 1 to 9. Although not shown in detail in FIGS. 1 to 13, DE 40 38 992 C2 describes this switch 26 as a switchable resistor. This fact forms the basis for the known principle.

In the practice, the pull-up and/or the pull-down of the central control unit will display a current limitation which is due to current source behaviour or resistance.

In the FIGS. of DE 40 38 992 C2 the pull-up and/or the pull-down are illustrated as a resistor. Thus it is necessary that the individual current of each participant is dimensioned at a smaller value than the value of the current limitation of the central control unit divided by the number of participants. First, the measuring current available for generating a useful signal is thus so small that despite the high measuring effort only faulty measurements may be expected. Second, this maximum usable measuring current depends on the number of bus participants.

According to the invention, this object is achieved with a method according to one of the independent claims, with individual embodiments being stated in the subclaims.

In the method for addressing the participants of a bus system, the central control unit connects the bus line to one potential of the operating voltage, while each participant tries to pull the bus line to a reference potential, normally the operating voltage, wherein, due to the current source behaviour of the switch placing the bus to the operating voltage, a current is detectable by a detector arranged in the bus line and associated with the participant. When the participant detects the decrease of current, said participant switches off its switch. Due to time-defined slow connection of the switched current sources, this process takes place sequentially within a group of participants until the last participant is reached. The detector associated with this participant does in no case detect a current, such that, after elapse of a predeterminable on-period, the switch of this participant is still open. The “open switch” state results from the first response of the detector, and this is the reason why in the above and the following description “open switch” means that the detector has responded. Thus one of the participants from the group of all participants is specified such that an address can now be allocated to this participant. During further addressing cycles the remaining participants are subjected to the same process, wherein the switch of the participant already addressed remains open all the time.

In particular, the method according to the invention offers the advantage that the static sum current of the controllable switches of all participants may be dimensioned to a higher value than the current which can be supplied by be resistor and/or the current source of the central control unit. In other words, the current flowing through a controllable switch may be larger that the current flowing off via the central control unit divided by the number of participants. Thus the following applies: I(27)>I(30)/n, wherein I(27) is the current flowing through the controllable switch, I(30) is the current flowing through the resistor or the current source, and n is the number of participants (see attached FIGS.).

Thus the useful signal to be employed for addressing purposes, i. e. the currents to be sensed by the detectors, is increased. As a result, the detectors are more inexpensive to produce since they need not be too sensitive. Further, the disturbance sensitivity in the addressing method according to the invention is improved.

Due to the fact that, according to the invention, the resistor used in the method is defined by a switch which is required for bus communication and which is controllable, realization of the inventive method does not require any additional component in comparison to a standard bus, which reduces the expenditure with regard to implementation of the method in an existing bus system.

In the variant according to claim 8 of the invention, the shunt resistors of the detectors used for current detection may have a relatively high resistance since they are not located in the bus line, and the useful signal for the detector is thus essentially increased, whereby the current influences may be reduced and therefore the detectors are considerably more inexpensive to produce.

If an analog-digital converter is arranged behind the shunt resistor and a digital comparator is used as a comparator, the threshold value can be parameterized in dependence on the application and the operating conditions, such as supply voltage, temperature and number of participants.

The method according to the invention need not be applied to all participants of the bus system. Further, the participants, to which the method is applied, may be located at any place/places of the bus system. In other words, the bus system may comprise participants at any place/places, which do not partake in the addressing process according to the invention, but do no disturb said process. These participants may then be addressed in a manner different from the inventive manner.

According to an advantageous variant of the invention, the modules of the central control unit are optionally provided as individual modules or in a combined form and/or as double modules, i. e. one module per bus connection, whereby both ends of the bus line are adapted to be operated by the central unit for analysis purposes and in the case of a fault (for example, open plug contact).

Various bus systems whose participants are adapted to be addressed in the inventive manner are shown in the drawings in which:

FIG. 1 shows a setup of a bus system for address allocation comprising four participants and having various optional additional modules, wherein the comparators required for bus communication are not shown since they are not involved in the address allocation process;

FIG. 2 shows a setup of the same system as shown in FIG. 1, but with inverse polarity of VDD1 and VDD2 to illustrate the fact that the polarity of VDD1 and VDD2 is not crucial, wherein both variants are mutually derivable by mirroring at the x-axis, and wherein only one participant is shown;

FIG. 3 shows a setup of a bus system for address allocation using the same structures for communication and address allocation, wherein only one participant is shown;

FIG. 4 shows a setup of the same system as shown in FIG. 3 but with inverse polarity;

FIG. 5 shows a setup of a bus system for address allocation with parallel arrangement of the current detectors and employment of an additional line, wherein two participants are shown;

FIG. 6 shows a bus system as that shown in FIG. 5 but with inverse polarity;

FIG. 7 shows a setup of a bus system for address allocation using a supply line for current detection; and

FIG. 8 shows a setup of the same system as shown in FIG. 7 but with inverse polarity.

Generally, in the bus systems shown in FIGS. 1 to 8 a central control unit 14 connects the bus line 12, when the participants 1 to 4 are addressed in the inventive manner, to one potential of the operating voltage VDD2, while each participant 1 to 4 tries to pull the bus line 12 to a reference potential, normally the operating voltage VDD1, wherein, due to the current source behaviour 27 of the switch 26 placing the bus to the operating voltage, a current is detectable by a detector 22 arranged in the bus line 12 and associated with the participant 1 to 4. When the participant detects this decrease of current with the aid of its drive unit 24, said participant switches off its switch 26. Due to time-defined slow connection of the switched current sources, this process takes place sequentially within a group of participants 1 to 4 until the last participant is reached. The detector 22 associated with this participant 4 does in no case detect a current, such that, after elapse of a predeterminable on-period, the switch 26 of this participant 1 to 4 is still open. Thus one of the participants from the group of all participants 1 to 4 is specified such that an address can now be allocated to this participant. During further addressing cycles the remaining participants are subjected to the same process, wherein the switch of the participant 4 already addressed remains open all the time.

Reference Numerals

14 Central control unit comprising

-   -   51 Pull-up resistor     -   52 Comparator for BUS operation     -   53 Drive of the physical BUS interface     -   30 Driver for BUS operation: switch with resistive or current         source behaviour

1 to 4 Participant comprising

-   -   50 Switch required for bus communication     -   22 Current detectors comprising         -   16 Shunt resistor         -   18 Comparator         -   20 Preamplifier         -   24 Control unit     -   26 Switch of each participant for impressing a measuring current     -   27 Resistance or current source behaviour of switch 26     -   28 Connecting line branching off the bus line 12

40,41 Switchable BUS pull-ups (optional additional modules)

21,41,54 Inverse-polarity protection diodes (optional additional modules) 

1. Method for addressing of the participants of a bus system which comprises a) a central control unit (14), b) a bus line (12) starting from the central control unit (14), and c) a plurality of participants (1 to 4) connected with the bus line (12), each participant comprising a detector (22) for detecting a current flow between this participant (1 to 4) and a participant (1 to 4) located closest to this participant and farther away from the central control unit (14), a controllable switch (26) for establishing a connection of the bus line (12) with a reference potential, a drive unit (24) for switching on and off the switch (26), inter alia on the basis of the output signal of the detector (22), and an address memory, wherein in the method d) in a first phase the central control unit (14) applies to the bus line (12) a closing signal for time-limited closing of the switches (26) of all participants (1 to 4) of the group of participants (1 to 4) not addressed so far for a predeterminable on-period (T), e) in a second phase the detectors (22) determine whether between respective adjacent participants (1 to 4) a current flows or does not flow, wherein f₁) in said second phase, with the exception of that participant (4) of the group of participants (1 to 4) not addressed so far which is arranged farthest away from the central control unit (14), the detectors (22) of all participants (1 to 4) not addressed so far detect a current flow to the respective participant (1 to 4) arranged farther away from the central control unit (14) and closest to the respective participant, f₂) consequently, the switches (26) of all participants (1 to 4) not addressed so far are opened, and g) the detector (22) of that participant (4) of the group of participants (1 to 4) not addressed so far, which is arranged farthest away from the central control unit (14), does, during the on-period (T), not detect a current flow to a participant (1 to 4) arranged farther away from the central control unit (14) and closest to the respective participant, and consequently, the switch (26) of this participant (4) not addressed so far is still closed upon elapse of the on-period (T) and is open only after elapse of the on-period (T), and h) in a third phase the central control unit (14) applies an address data signal to the bus line (12), wherein said address data signal is stored in the address memory of that participant (4) of the group of participants (1 to 4) not addressed so far whose switch (26) has changed into the open state since the on-period (T) has elapsed, this participant (1 to 4) thus being addressed, wherein in this method i) for each participant (1 to 4) the controllable switch (26), in addition to a switch (50) required for bus communication, is integrated in the system, j) a resistor (30) of the central control unit (14) partaking in the method, in addition to another resistor (51) required for bus communication which may be arranged in the central control unit (14), is integrated in the system, k) the resistor (30) partaking in the method is defined by a switch required for bus communication, said switch being controllable (FIG. 1), l) the controllable switch (26) of each participant (1 to 4) is not only resistive but has a defined resistance (27) or current source behaviour (27), which is approximately identical for all participants (1 to 4), m) activation of the controllable switches (26,27) of all participants (1 to 4) is effected simultaneously, n) activation of the controllable switches (26,27) of all participants (1 to 4) leads to a relatively slow rise of the currents in the current-determining elements of the controllable switches (26,27), as a result of which the sum current on the line (12) rises relatively slowly either, o) deactivation of the controllable switches (26,27) of all participants (1 to 4) is initiated directly or with a time delay by the response of the detector (22), as a result of which the sum current of all participants (1 to 4) is reduced due to the lack of the load of this participant (1 to 4), p) this deactivation process takes place as a chain reaction starting with the participant (1) located closest to the central control unit (14), q) the sum current on the line (12) rises slowly due to the slow energizing, relative to the low speed of response of the detectors (22), of the controllable switches (26,27), but, at the same time, is stepwise reduced due to the deactivation processes triggered by the detectors (22), as a result of which the sum current remains limited, r) whereby the current-carrying capacity of the resistor or current source (30) of the central control unit (14) partaking in the method is always larger than the sum of the instantaneous currents of the controllable switches (26,27) of all participants (1 to 4), as a result of which the controllable switches (26,27) of all participants remain in a position to impress the currents provided by the invention.
 2. Method according to claim 1, characterized in that for all participants (1 to 4) of the group of participants (1 to 4) not addressed so far addressing takes place in a plurality of addressing cycles.
 3. Method according to claim 2, characterized in that the on-period (T) is reduced from address cycle to address cycle.
 4. Method for addressing the participants of a bus system which comprises a) a bus line (12), b) a plurality of participants (1 to 4) connected with the bus line (12), each participant comprising a detector (22) for detecting a current flow between this participant (1 to 4) and the participant (1 to 4) located closest to this participant, a controllable switch (26) for establishing a connection of the bus line (12) with a reference potential, a drive unit (24) for switching on and off the switch (26), inter alia on the basis of the output signal of the detector (22), and an address memory, wherein in the method c) the drive units (24) of all participants (1 to 4) of the group of participants (1 to 4) not addressed so far switch on the switches (26) for a predeterminable on-period (T), d) within the on-period (T) the switches (26) of those participants (1 to 4) are opened whose detectors (22) detect a current flow to the respective adjacent participant (1 to 4), e) wherein the switch (26) of one of the participants (1 to 4) is still open upon elapse of the on-period (T), and f) wherein an address is placed into the address memory of this participant (1 to 4), this participant (1 to 4) thus being addressed, wherein in this method the following is provided as a novelty within the purview of the invention g) for each participant (1 to 4) the controllable switch (26), in addition to a switch (50) required for bus communication, is integrated in the system, h) a resistor (30) of the central control unit (14) partaking in the method, in addition to another resistor (51) required for bus communication which may be arranged in the central control unit (14), is integrated in the system, i) the resistor (30) partaking in the method is defined by a switch required for bus communication, said switch being controllable (FIG. 1), j) the controllable switch (26) of each participant (1 to 4) is not only resistive but has a defined resistance (27) or current source behaviour (27), which is approximately identical for all participants (1 to 4), k) activation of the controllable switches (26,27) of all participants (1 to 4) is effected simultaneously, l) activation of the controllable switches (26,27) of all participants (1 to 4) leads to a relatively slow rise of the currents in the current-determining elements (27) of the controllable switches (26,27), as a result of which the sum current on the line (12) rises relatively slowly either, m) deactivation of the controllable switches (26,27) of all participants (1 to 4) is initiated directly or with a time delay by the response of the detector (22), as a result of which the sum current of all participants (1 to 4) is reduced due to the lack of the load of this participant (1 to 4), n) this deactivation process takes place as a chain reaction starting with the participant (1) located closest to the central control unit (14), o) the sum current on the line (12) rises slowly due to the slow energizing, relative to the low speed of response of the detectors (22), of the controllable switches (26,27), but, at the same time, is stepwise reduced due to the deactivation processes triggered by the detectors (22), as a result of which the sum current remains limited by the method according to the invention, p) whereby the current-carrying capacity of the resistor or current source (30) of the central control unit (14) partaking in the method is always larger than the sum of the instantaneous currents of the controllable switches (26,27) of all participants (1 to 4), as a result of which the controllable switches (26,27) of all participants remain in a position to impress the currents provided by the invention.
 5. Method according to one of claims 1 to 4, characterized in that the bus line (12) has connected thereto one or a plurality of central control units (14), and that at least one of these central control units (14) initiates closing of the switches (26) of all participants (1 to 4) of the group of participants (1 to 4) not addressed so far.
 6. Method according to one of claims 1 to 5, characterized in that the drive units (24) of all participants (1 to 4), for the purpose of synchronizing the closing process of the switches (26) for the duration of the on-period (T), close the switches (26) of all participants (1 to 4) within a predeterminable period (T1) and then open them again, wherein opening of the last switch (26) is recognized and this point of time is the synchronization time (T2), wherein, after elapse of another period (T3), all switches (26) are closed in a synchronized manner for the duration of the on-period (T).
 7. Method according to one of claims 1 to 6, characterized in that the detectors (22) are connected in series in the bus line (12), and that the switch (26) of each participant (1 to 4) is arranged in a connecting line (28) which branches off the bus line (12) before the detector (22) of this participant (1 to 4) as seen from the central control unit (14).
 8. Method for addressing the participants of a bus system which comprises a) a central control unit (14), b) a bus line (12) starting from the central control unit (14), and c) a plurality of participants (1 to 4) connected with the bus line (12), each participant comprising a detector (22) for detecting a current flow between this participant (1 to 4) and a participant (1 to 4) located closest to this participant and farther away from the central control unit (14), a controllable switch (26) for establishing a connection of the bus line (12) with a reference potential, a drive unit (24) for switching on and off the switch (26), inter alia on the basis of the output signal of the detector (22), and an address memory, wherein in the method d) in a first phase the central control unit (14) applies to the bus line (12) a closing signal for time-limited closing of the switches (26) of all participants (1 to 4) of the group of participants (1 to 4) not addressed so far for a predeterminable on-period (T), e) in a second phase the detectors (22) determine whether between respective adjacent participants (1 to 4) a current flows or does not flow, wherein f) in said second phase, with the exception of that participant (4) of the group of participants (1 to 4) not addressed so far which is arranged farthest away from the central control unit (14), the detectors (22) of all participants (1 to 4) not addressed so far detect a current flow to the participant (1 to 4) arranged farther away from the central control unit (14) and closest to the respective participant, g) the detector (22) of that participant (4) of the group of participants (1 to 4) not addressed so far, which is arranged farthest away from the central control unit (14), does, during the on-period (T), not detect a current flow to a participant (1 to 4) arranged farther away from the central control unit (14) and closest to the respective participant, and consequently, the switch (26) of this participant (4) not addressed so far is still closed upon elapse of the on-period (T) and is opened only upon elapse of the on-period (T), and h) in a third phase the central control unit (14) applies an address data signal to the bus line (12), wherein said address data signal is stored in the address memory of that participant (4) of the group of participants (1 to 4) not addressed so far whose switch (26) has changed into the open state since the on-period (T) has elapsed, this participant (1 to 4) thus being addressed, wherein in this method i) for each participant (1 to 4) the controllable switch (26), in addition to a switch (50) required for bus communication, is integrated in the system, j) a resistor (30) of the central control unit (14) partaking in the method, in addition to another resistor (51) required for bus communication which may be arranged in the central control unit (14), is integrated in the system, k) the controllable switch (26) of each participant (1 to 4) is not only resistive but has a defined resistance (27) or current source behaviour (27), which is approximately identical for all participants (1 to 4), and l) activation of the controllable switches (26,27) of all participants (1 to 4) is effected simultaneously, m) the detectors (22) and the switches (26) are connected in series in connecting lines (28) which branch off a line carrying a supply voltage (VDD2), n) in each connecting line the detector (22) and the switch (26) of two respective adjacent participants (1 to 4) are arranged, and o) the detector (22) is associated with the participant (1 to 4) arranged closer to the central control unit (14), and the switch (26) is associated with the participant (1 to 4) arranged farther away from the central control unit (14) (FIGS. 5 and 6).
 9. Method according to claim 8, characterized in that for all participants (1 to 4) of the group of participants (1 to 4) not addressed so far addressing takes place in a plurality of addressing cycles.
 10. Method according to claim 9, characterized in that the on-period (T) is reduced from address cycle to address cycle.
 11. Method for addressing the participants of a bus system which comprises a) a bus line (12), b) a plurality of participants (1 to 4) connected with the bus line (12), each participant comprising a detector (22) for detecting a current flow between this participant (1 to 4) and the participant (1 to 4) located closest to this participant, a controllable switch (26) for establishing a connection of the bus line (12) with a reference potential, a drive unit (24) for switching on and off the switch (26), inter alia on the basis of the output signal of the detector (22), and an address memory, wherein in the method c) the drive units (24) of all participants (1 to 4) of the group of participants (1 to 4) not addressed so far switch on the switches (26) for a predeterminable on-period (T), d) wherein the switch (26) of one of the participants (1 to 4) is still open during the on-period (T), and e) wherein an address is stored in the address memory of this participant (1 to 4), this participant (1 to 4) thus being addressed, wherein in this method f) for each participant (1 to 4) the controllable switch (26), in addition to a switch (50) required for bus communication, is integrated in the system,. g) a resistor (30) of the central control unit (14) partaking in the method, in addition to another resistor (51) required for bus communication which may be arranged in the central control unit (14), is integrated in the system, h) the controllable switch (26) of each participant (1 to 4) is not only resistive but has a defined resistance (27) or current source behaviour (27), which is approximately identical for all participants (1 to 4), and i) activation of the controllable switches (26,27) of all participants (1 to 4) is effected simultaneously, j) the detectors (22) and the switches (26) are connected in series in connecting lines (28) which branch off a line carrying a supply voltage (VDD2), k) in each connecting line the detector (22) and the switch (26) of two respective adjacent participants (1 to 4) are arranged, and l) the detector (22) is associated with the participant (1 to 4) arranged closer to the central control unit (14), and the switch (26) is associated with the participant (1 to 4) arranged farther away from the central control unit (14) (FIGS. 5 and 6).
 12. Method according to one of claims 8 to 11, characterized in that the bus line (12) has connected thereto one or a plurality of central control units (14), and that at least one of these central control units (14) initiates closing of the switches (26) of all participants (1 to 4) of the group of participants (1 to 4) not addressed so far.
 13. Method according to one of claims 8 to 12, characterized in that the drive units (24) of all participants (1 to 4), for the purpose of synchronizing the closing process of the switches (26) for the duration of the on-period (T), close the switches (26) of all participants (1 to 4) within a predeterminable period (T1) and then open them again, wherein opening of the last switch (26) is recognized and this point of time is the synchronization time (T2), wherein, after elapse of another period (T3), all switches (26) are closed in a synchronized manner for the duration of the on-period (T).
 14. Method according to one of claims 8 to 13, characterized in that the detectors (22) are connected in series in the bus line (12), and that the switch (26) of each participant (1 to 4) is arranged in a connecting line (28) which branches off the bus line (12) before the detector (22) of this participant (1 to 4) as seen from the central control unit (14).
 15. Method according to one of claims 1 to 14, characterized in that the participant (1 to 4) connected to the bus line (12) at a location farthest away from the central control unit (14) does not comprise a detector (22).
 16. Method according to one of claims 1 to 15, characterized in that each detector (22) comprises a shunt resistor (16) and a comparator (18) for comparing the voltage drop (U_(s)) across the shunt resistor with a reference value (V_(ref)).
 17. Method according to claim 16, characterized in that a preamplifier (20) for amplifying the voltage drop (U_(s)) is arranged before the comparator (18).
 18. Method according to claim 16 or 17, characterized in that an analog-digital converter is arranged behind the shunt resistor (16).
 19. Method according to claim 18, characterized in that the comparator is a digital comparator.
 20. Method according to one of claims 16 to 19, characterized in that the shunt resistor (16) is integrated in the line (12), as a result of which in the individual participant only the detection of the voltage drop takes place.
 21. Method according to one of claims 16 to 19, characterized in that the shunt resistor (16) is integrated in each participant (1 to 4), as a result of which the complete current detection takes place in each participant (1 to 4).
 22. Method according to one of claims 16 to 19, characterized in that the shunt resistor is integrated in a plug connection between bus line (12) and participant (1 to 4), as a result of which neither in the line nor in the participant (1 to 4) any expenditure for a resistor (16) is necessary.
 23. Method according to one of claims 16 to 18, characterized in that the shunt resistor in each participant (1 to 4) is integrated in an existing semiconductor component, as a result of which this component is inexpensive to produce and fewer quality problems occur.
 24. Method according to one of claims 16 to 19, characterized in that the shunt resistor (16) in each participant (1 to 4) is integrated in an existing semiconductor component and is defined by internal wiring, as a result of which this component is inexpensive to produce and fewer quality problems occur.
 25. Method according to one of claims 1 to 19, characterized in that in bus systems in which each participant (1 to 4) includes an additional pull-up or pull-down (41) in the form of a resistor or a current source, said participant is adapted to be deactivated by a switch (40) for the purpose of being addressed by the drive unit (24), as a result of which said components (41) do not exert any disturbing influences on the addressing process.
 26. Method according to one of claims 1 to 19, characterized in that in-verse-polarity protection diodes (31,41,54) are arranged in individual or all participants (1 to 4) without the efficiency of the addressing process being affected.
 27. Method according to one of claims 1 to 19, characterized in that the bus system comprises at any place/places participants which do not partake in the addressing process but do no disturb said process.
 28. Method according to one of claims 1 to 19, characterized in that the bus line (12) is routed via a return line to both sides of the central control unit (14).
 29. Method according to claim 28, characterized in that the modules (51, 52,30) of the central control unit (14) are, at option, provided twice, as a result of which both ends of the bus line (12) can be operated by the central control unit (14) for analysis purposes or in the case of malfunction.
 30. Method according to claim 28, characterized in that the return line of the main cable line establishes a connection with the bus line (12) of exactly one sub-cable line, as a result of which all participants in the sub-cable line are located behind the last participant of the main cable line as seen, from the electrical point of view, from the side of the central control unit.
 31. Method according to claim 28 and 30, characterized in that the sub-cable line, too, is provided with a return line, and a connection with the bus line (12) of exactly one further subordinate sub-cable line can be established, as a result of which the method can be continued in any way desired, and tree-like cable harnesses can be built up despite the sequential electrical arrangement of the participants.
 32. Method according to one of claims 1 to 31, characterized in that the reference potential for the switch (26) of each participant is the supply voltage (VDD1) of said participant, wherein the polarity between the supply voltages (VDD1,VDD2) is not crucial (FIGS. 1,2).
 33. Method according to one of claims 1 to 32, characterized in that the method is not carried out on the bus line (12) but on a line dedicated for addressing purposes.
 34. Method according to one of claims 1 to 32, characterized in that the method is not carried out on the bus line (12) but on a line carrying the supply voltage (VDD2), as a result of which in the central control unit (14), the resistor and/or the current source (30) can be substituted by a conducting connection (FIGS. 7 and 8).
 35. Method according to one of claims 1 to 34, characterized in that the polarity between the lines carrying the supply voltages (VDD1,VDD2) is arbitrary (FIGS. 1,2,7,8).
 36. Method according to one of claims 1 to 35, characterized in that the method is applied to a wire of a multi-wire bus system.
 37. Method according to one of claims 1 to 31, characterized in that the method is applied to multi-wire bus systems, and the controllable switches (26) and the current-determining elements (27) of each participant (14) are not connected to the reference potential but to a second bus line, wherein in the method the central control unit places this second bus line to a reference potential, normally VDD1, and in the central control unit, this is realized via a current-limiting switch or a switched resistor, as a result of which, according to the invention, malfunctions and voltage offsets on the lines carrying the supply voltages (VDD1,VDD2) in the cable line are no longer relevant.
 38. Method according to claim 37, characterized in that both bus lines employed are provided with current detectors (22) and are evaluated.
 39. Method according to one of claims 1 to 30, characterized in that the structures required for bus communication in the participants are employed for carrying out the addressing process (FIGS. 3 and 4), as a result of which in the method the current direction in the detectors (22) is the same as in the case of a standard bus communication, and the individual participants are more inexpensive to produce.
 40. Method according to one of claims 1 to 40, characterized in that in bus systems in which each participant (1 to 4) comprises an additional pull-up or pull-down (41) in the form of a resistor or a current source, said participant is adapted to be deactivated by a switch (40) for the purpose of being addressed by the drive unit (24), as a result of which said components (41) do not exert any disturbing influences on the addressing process.
 41. Method according to one of claims 1 to 40, characterized in that in-verse-polarity protection diodes (31,41,54) are arranged in individual or all participants (1 to 4) without the efficiency of the addressing process being affected. 